Brake mechanism for power equipment

ABSTRACT

Brake pawls for use in safety systems for power equipment are disclosed. The brake pawls include an energy-absorbing region. The energy absorbing regions may include a deformable or collapsible region made from apertures in the brake pawl or from collapsible members or from materials of differing hardnesses, strengths, or structures.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.11/401,050, filed Apr. 10, 2006, which is a continuation of a number ofapplications including U.S. patent application Ser. No. 09/929,241,filed Aug. 13, 2001, issuing as U.S. Pat. No. 7,024,975 on Apr. 11,2006, which in turn claimed the benefit of and priority from thefollowing U.S. Provisional Patent Applications: Ser. No. 60/225,056,filed Aug. 14, 2000, Ser. No. 60/225,057, filed Aug. 14, 2000, Ser. No.60/225,058, filed Aug. 14, 2000, Ser. No. 60/225,059, filed Aug. 14,2000, Ser. No. 60/225,089, filed Aug. 14, 2000, Ser. No. 60/225,094,filed Aug. 14, 2000, Ser. No. 60/225,169, filed Aug. 14, 2000, Ser. No.60/225,170, filed Aug. 14, 2000, Ser. No. 60/225,200, filed Aug. 14,2000, Ser. No. 60/225,201, filed Aug. 14, 2000, Ser. No. 60/225,206,filed Aug. 14, 2000, Ser. No. 60/225,210, filed Aug. 14, 2000, Ser. No.60/225,211, filed Aug. 14, 2000, and Ser. No. 60/225,212, filed Aug. 14,2000.

This application is also a continuation of U.S. patent application Ser.No. 10/341,260, filed Jan. 13, 2003, which claims the benefit of andpriority from U.S. Provisional Patent Application Ser. No. 60/351,797,filed Jan. 25, 2002.

This application is also a continuation of U.S. patent application Ser.No. 11/447,449, filed Jan. 5, 2006, which is a continuation of U.S.patent application Ser. No. 09/676,190, filed Sep. 29, 2000, issuing asU.S. Pat. No. 7,055,417 on Jun. 6, 2006, which in turn claimed thebenefit of and priority from U.S. Provisional Patent Application Ser.No. 60/157,340, filed Oct. 1, 1999 and U.S. Provisional PatentApplication Ser. No. 60/182,866, filed Feb. 16, 2000.

All of the above applications are hereby incorporated by reference intheir entireties.

FIELD

The present disclosure relates to safety systems for power equipment,and more particularly to a brake mechanism for use on power equipment,such as woodworking machines.

BACKGROUND

Safety systems are often employed with power equipment such as tablesaws, miter saws, band saws, jointers, shapers, circular saws and otherwoodworking machinery, to minimize the risk of injury when using theequipment. Probably the most common safety feature is a guard thatphysically blocks an operator from making contact with dangerouscomponents of machinery, such as belts, shafts or blades. In many cases,guards effectively reduce the risk of injury, however, there are manyinstances where the nature of the operations to be performed precludesusing a guard that completely blocks access to hazardous machine parts.

The present disclosure discloses a safety system, and power equipmentincorporating a safety system, that includes a brake mechanism adaptedto engage the blade or other cutting tool to protect the user againstserious injury if a dangerous, or triggering, condition, such as contactbetween the user's body and the blade or other cutting tool, occurs. Thebrake mechanism includes a pawl that is biased to engage and quicklystop the blade or other cutting tool.

Various brake pawls are disclosed herein for use in safety systems thatinclude a brake mechanism adapted to engage a blade or other cuttingtool to protect the user against serious injury if a dangerous, ortriggering, condition occurs, such as contact between the user's bodyand the blade or other cutting element.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic block diagram of a machine with a fast-actingsafety system.

FIG. 2 is a schematic diagram of an exemplary safety system in thecontext of a machine having a circular blade.

FIG. 3 is a side elevation view of a brake mechanism, including a pawl.

FIG. 4 is a side elevation view of a portion of another brake mechanism.

FIG. 5 is a side elevation view of another pawl.

FIG. 6 is a side elevation view of another pawl.

FIG. 7 is an isometric view of another pawl.

FIG. 8 is a side elevation view of another pawl.

FIG. 9 is a side elevation view of another pawl.

FIG. 10 is a side elevation view of another pawl.

FIG. 11 is a side elevation view of another pawl.

FIG. 12 is a side elevation view of another pawl.

FIG. 13 is a side elevation view of another pawl.

FIG. 14 is a side elevation view of another pawl.

FIG. 15 is a side elevation view of another pawl.

FIG. 16 is a side elevation view of another pawl.

FIG. 17 is a side elevation view of another brake mechanism.

FIG. 18 is a side elevation view of another brake mechanism.

FIG. 19 is a side elevation view of another brake mechanism.

FIG. 20 is a side elevation view of another brake mechanism.

FIG. 21 is a top plan view of the brake mechanism of FIG. 20.

FIG. 22 is a side elevation view of a brake mechanism with atranslational pawl.

FIG. 23 is a side elevation view of another brake mechanism with atranslational pawl.

FIG. 24 is a side elevation view of another brake mechanism with atranslational pawl.

FIG. 25 is a side elevation view of another brake mechanism with atranslational pawl.

FIG. 26 is a side elevation view of a brake mechanism that includesplural pawls.

FIG. 27 is a fragmentary side elevation view of another brake mechanismthat includes plural pawls.

FIG. 28 is a top plan view of another brake mechanism.

FIG. 29 shows a brake pawl with a deformable or collapsible region.

FIG. 30 shows the brake pawl of FIG. 29 with the deformable orcollapsible region collapsed.

FIG. 31 shows a brake pawl with a deformable or collapsible region madeof an elongate aperture.

FIG. 32 shows the brake pawl of FIG. 31 with the deformable orcollapsible region collapsed.

FIG. 33 shows a brake pawl with a deformable or collapsible regionpositioned at an angle relative to the elongate axis of the brake pawl.

FIG. 34 shows a brake pawl with a deformable or collapsible regionincluding a collapsible member.

FIG. 35 shows a brake pawl with a deformable or collapsible regionincluding a plurality of collapsible members.

FIG. 36 shows a brake pawl with a “T” shaped end having members that maybend or deform.

DETAILED DESCRIPTION

A machine is generally at 10. Machine 10 may be any of a variety ofdifferent machines adapted for cutting workpieces, such as wood,including a table saw, miter saw (chop saw), radial arm saw, circularsaw, band saw, jointer, planer, etc. Machine 10 includes an operativestructure 12 having a cutting tool 14 and a motor assembly 16 adapted todrive the cutting tool. Machine 10 also includes a safety system 18configured to minimize the potential of a serious injury to a personusing machine 10. Safety system 18 is adapted to detect the occurrenceof one or more dangerous, or triggering, conditions during use ofmachine 10. If such a dangerous condition is detected, safety system 18is adapted to engage operative structure 12 to limit any injury to theuser caused by the dangerous condition.

Machine 10 also includes a suitable power source 20 to provide power tooperative structure 12 and safety system 18. Power source 20 may be anexternal power source such as line current, or an internal power sourcesuch as a battery. Alternatively, power source 20 may include acombination of both external and internal power sources. Furthermore,power source 20 may include two or more separate power sources, eachadapted to power different portions of machine 10.

It will be appreciated that operative structure 12 may take any one ofmany different forms, depending on the type of machine 10. For example,operative structure 12 may include a stationary housing configured tosupport motor assembly 16 in driving engagement with cutting tool 14.Alternatively, operative structure 12 may include a movable structureconfigured to carry cutting tool 14 between multiple operatingpositions. As a further alternative, operative structure 12 may includeone or more transport mechanisms adapted to convey a workpiece towardand/or away from cutting tool 14.

Motor assembly 16 includes one or more motors adapted to drive cuttingtool 14. The motors may be either directly or indirectly coupled to thecutting tool, and may also be adapted to drive workpiece transportmechanisms. Cutting tool 14 typically includes one or more blades orother suitable cutting implements that are adapted to cut or removeportions from the workpieces. The particular form of cutting tool 14will vary depending upon the various embodiments of machine 10. Forexample, in table saws, miter saws, circular saws and radial arm saws,cutting tool 14 will typically include one or more circular rotatingblades having a plurality of teeth disposed along the perimetrical edgeof the blade. For a jointer or planer, the cutting tool typicallyincludes a plurality of radially spaced-apart blades. For a band saw,the cutting tool includes an elongate, circuitous tooth-edged band.

Safety system 18 includes a detection subsystem 22, a reaction subsystem24 and a control subsystem 26. Control subsystem 26 may be adapted toreceive inputs from a variety of sources including detection subsystem22, reaction subsystem 24, operative structure 12 and motor assembly 16.The control subsystem may also include one or more sensors adapted tomonitor selected parameters of machine 11. In addition, controlsubsystem 26 typically includes one or more instruments operable by auser to control the machine. The control subsystem is configured tocontrol machine 10 in response to the inputs it receives.

Detection subsystem 22 is configured to detect one or more dangerous, ortriggering, conditions during use of machine 10. For example, thedetection subsystem may be configured to detect that a portion of theuser's body is dangerously close to, or in contact with, a portion ofcutting tool 14. As another example, the detection subsystem may beconfigured to detect the rapid movement of a workpiece due to kickbackby the cutting tool, as is described in U.S. Provisional PatentApplication Ser. No. 60/182,866, the disclosure of which is hereinincorporated by reference. In some embodiments, detection subsystem 22may inform control subsystem 26 of the dangerous condition, which thenactivates reaction subsystem 24. In other embodiments, the detectionsubsystem may be adapted to activate the reaction subsystem directly.

Once activated in response to a dangerous condition, reaction subsystem24 is configured to engage operative structure 12 quickly to preventserious injury to the user. It will be appreciated that the particularaction to be taken by reaction subsystem 24 will vary depending on thetype of machine 10 and/or the dangerous condition that is detected. Forexample, reaction subsystem 24 may be configured to do one or more ofthe following: stop the movement of cutting tool 14, disconnect motorassembly 16 from power source 20, place a barrier between the cuttingtool and the user, or retract the cutting tool from its operatingposition, etc. The reaction subsystem may be configured to take acombination of steps to protect the user from serious injury. Placementof a barrier between the cutting tool and teeth is described in moredetail in U.S. Provisional Patent Application Ser. No. 60/225,206,entitled “Cutting Tool Safety System,” filed Aug. 14, 2000 by SD3, LLC,the disclosure of which is herein incorporated by reference. Retractionof the cutting tool from its operating position is described in moredetail in U.S. Provisional Patent Application Ser. No. 60/225,089,entitled “Retraction System For Use In Power Equipment,” filed Aug. 14,2000 by SD3, LLC, the disclosure of which is herein incorporated byreference.

The configuration of reaction subsystem 24 typically will vary dependingon which action(s) are taken. In the exemplary embodiment depicted inFIG. 1, reaction subsystem 24 is configured to stop the movement ofcutting tool 14 and includes a brake mechanism 28, a biasing mechanism30, a restraining mechanism 32, and a release mechanism 34. Brakemechanism 28 is adapted to engage operative structure 12 under theurging of biasing mechanism 30. During normal operation of machine 10,restraining mechanism 32 holds the brake mechanism out of engagementwith the operative structure. However, upon receipt of an activationsignal by reaction subsystem 24, the brake mechanism is released fromthe restraining mechanism by release mechanism 34, whereupon, the brakemechanism quickly engages at least a portion of the operative structureto bring the cutting tool to a stop.

It will be appreciated by those of skill in the art that the exemplaryembodiment depicted in FIG. 1 and described above may be implemented ina variety of ways depending on the type and configuration of operativestructure 12. Turning attention to FIG. 2, one example of the manypossible implementations of safety system 18 is shown. System 18 isconfigured to engage an operative structure having a cutting tool in theform of a circular blade 40 mounted on a rotating shaft or arbor 42.Blade 40 includes a plurality of cutting teeth (not shown) disposedaround the outer edge of the blade. As described in more detail below,braking mechanism 28 is adapted to engage the teeth of blade 40 and stopthe rotation of the blade. U.S. Provisional Patent Application Ser. No.60/225,210, entitled “Translation Stop For Use In Power Equipment,”filed Aug. 14, 2000 by SD3, LLC, the disclosure of which is hereinincorporated by reference, describes other systems for stopping themovement of the cutting tool. U.S. Provisional Patent Application Ser.No. 60/225,058, entitled “Table Saw With Improved Safety System,” filedAug. 14, 2000 by SD3, LLC and U.S. Provisional Patent Application Ser.No. 60/225,057, entitled “Miter Saw With Improved Safety System,” filedAug. 14, 2000 by SD3, LLC, the disclosures of which are hereinincorporated by reference, describe safety system 18 in the context ofparticular types of machines 10.

In the exemplary implementation, detection subsystem 22 is adapted todetect the dangerous condition of the user coming into contact withblade 40. The detection subsystem includes a sensor assembly, such ascontact detection plates 44 and 46, capacitively coupled to blade 40 todetect any contact between the user's body and the blade. Typically, theblade, or some larger portion of cutting tool 14 is electricallyisolated from the remainder of machine 10. Alternatively, detectionsubsystem 22 may include a different sensor assembly configured todetect contact in other ways, such as optically, resistively, etc. Inany event, the detection subsystem is adapted to transmit a signal tocontrol subsystem 26 when contact between the user and the blade isdetected. Various exemplary embodiments and implementations of detectionsubsystem 22 are described in more detail in U.S. Provisional PatentApplication Ser. No. 60/225,200, entitled “Contact Detection System ForPower Equipment,” filed Aug. 14, 2000 by SD3, LLC and U.S. ProvisionalPatent Application Ser. No. 60/225,211, entitled “Apparatus And MethodFor Detecting Dangerous Conditions In Power Equipment,” filed Aug. 14,2000 by SD3, LLC, the disclosures of which are herein incorporated byreference.

Control subsystem 26 includes one or more instruments 48 that areoperable by a user to control the motion of blade 40. Instruments 48 mayinclude start/stop switches, speed controls, direction controls, etc.Control subsystem 26 also includes a logic controller 50 connected toreceive the user's inputs via instruments 48. Logic controller 50 isalso connected to receive a contact detection signal from detectionsubsystem 22. Further, the logic controller may be configured to receiveinputs from other sources (not shown) such as blade motion sensors,workpiece sensors, etc. In any event, the logic controller is configuredto control operative structure 12 in response to the user's inputsthrough instruments 48. However, upon receipt of a contact detectionsignal from detection subsystem 22, the logic controller overrides thecontrol inputs from the user and activates reaction subsystem 24 to stopthe motion of the blade. Various exemplary embodiments andimplementations of control subsystem 26 are described in more detail inU.S. Provisional Patent Application Ser. No. 60/225,059, entitled “LogicControl For Fast Acting Safety System,” filed Aug. 14, 2000 by SD3, LLCand U.S. Provisional Patent Application Ser. No. 60/225,094, entitled“Motion Detecting System For Use In Safety System For Power Equipment,”filed Aug. 14, 2000 by SD3, LLC, the disclosures of which are hereinincorporated by reference.

In the exemplary implementation, brake mechanism 28 includes a pawl 60mounted adjacent the edge of blade 40 and selectively moveable to engageand grip the teeth of the blade. Pawl 60 may be constructed of anysuitable material adapted to engage and stop the blade. As one example,the pawl may be constructed of a relatively high strength thermoplasticmaterial such as polycarbonate, ultrahigh molecular weight polyethylene(UHMW) or Acrylonitrile Butadiene Styrene (ABS), etc., or a metal suchas aluminum, etc. It will be appreciated that the construction of pawl60 will vary depending on the configuration of blade 40. In any event,the pawl is urged into the blade by a biasing mechanism in the form of aspring 66. In the illustrative embodiment shown in FIG. 2, pawl 60 ispivoted into the teeth of blade 40. It should be understood that slidingor rotary movement of pawl 60 may also be used. The spring is adapted tourge pawl 60 into the teeth of the blade with sufficient force to gripthe blade and quickly bring it to a stop.

The pawl is held away from the edge of the blade by a restrainingmechanism in the form of a fusible member 70. The fusible member isconstructed of a suitable material adapted to restrain the pawl againstthe bias of spring 66, and also adapted to melt under a determinedelectrical current density. Examples of suitable materials for fusiblemember 70 include NiChrome wire, stainless steel wire, etc. The fusiblemember is connected between the pawl and a contact mount 72. Preferably,fusible member 70 holds the pawl relatively close to the edge of theblade to reduce the distance the pawl must travel to engage the blade.Positioning the pawl relatively close to the edge of the blade reducesthe time required for the pawl to engage and stop the blade. Typically,the pawl is held approximately 1/32-inch to ¼-inch from the edge of theblade by fusible member 70, however other pawl-to-blade spacings mayalso be used.

Pawl 60 is released from its unactuated, or cocked, position to engageblade 40 by a release mechanism in the form of a firing subsystem 76.The firing subsystem is coupled to contact mount 72, and is configuredto melt fusible member 70 by passing a surge of electrical currentthrough the fusible member. Firing subsystem 76 is coupled to logiccontroller 50 and activated by a signal from the logic controller. Whenthe logic controller receives a contact detection signal from detectionsubsystem 22, the logic controller sends an activation signal to firingsubsystem 76, which melts fusible member 70, thereby releasing the pawlto stop the blade. Various exemplary embodiments and implementations ofreaction subsystem 24 are described in more detail in U.S. ProvisionalPatent Application Ser. No. 60/225,056, entitled “Firing Subsystem ForUse In Fast Acting Safety System,” filed Aug. 14, 2000 by SD3, LLC andU.S. Provisional Patent Application Ser. No. 60/225,170, entitled“Spring-Biased Brake Mechanism for Power Equipment,” filed Aug. 14, 2000by SD3, LLC, the disclosures of which are herein incorporated byreference.

It will be appreciated that activation of the brake mechanism willrequire the replacement of one or more portions of safety system 18. Forexample, pawl 60 and fusible member 70 typically must be replaced beforethe safety system is ready to be used again. Thus, it may be desirableto construct one or more portions of safety system 18 in a cartridgethat can be easily replaced. For example, in the exemplaryimplementation depicted in FIG. 2, safety system 18 includes areplaceable cartridge 80 having a housing 82. Pawl 60, spring 66,fusible member 70 and contact mount 72 are all mounted within housing82. Alternatively, other portions of safety system 18 may be mountedwithin the housing. In any event, after the reaction system has beenactivated, the safety system can be reset by replacing cartridge 80. Theportions of safety system 18 not mounted within the cartridge may bereplaced separately or reused as appropriate. Various exemplaryembodiments and implementations of a safety system using a replaceablecartridge are described in more detail in U.S. Provisional PatentApplication Ser. No. 60/225,201, entitled “Replaceable Brake MechanismFor Power Equipment,” filed Aug. 14, 2000 by SD3, LLC and U.S.Provisional Patent Application Ser. No. 60/225,212, entitled “BrakePositioning System,” filed Aug. 14, 2000 by SD3, LLC, the disclosures ofwhich are herein incorporated by reference.

While one particular implementation of safety system 18 has beendescribed, it will be appreciated that many variations and modificationsare possible. Many such variations and modifications are described inU.S. Provisional Patent Application Ser. Nos. 60/182,866 and 60/157,340,the disclosures of which are herein incorporated by reference.

As discussed, safety system 18 includes a brake mechanism 28 that isadapted to stop the cutting tool, thereby preventing or reducing injuryto the user. As also discussed previously, brake mechanism 28 mayinclude at least one pawl 60 adapted to engage the cutting tool to stopthe rotation thereof. For purposes of the following discussion, cuttingtool 14 will be described in the context of a blade 40, such as on atable saw, miter saw, circular saw or the like. It should be understoodthat blade 40 may include single blades, such as plywood orcarbide-tipped blades, or an assembly of several blades, such as a dadoblade.

As discussed, pawl 60 may be made of any suitable material that iscapable of quickly stopping the blade or other cutting tool within thedesired time increment, such as less than 5 milliseconds, andpreferably, 3 milliseconds or less. The above examples of thermoplasticand metallic materials have proven effective, although other materialsmay be used so long as they are able to stop the blade within thedesired time increment. Preferably, the pawl is formed of a materialthat does not damage the machine, and even more preferably, the pawl isformed of a material that does not damage the cutting tool. The pawl maybe formed by any suitable method, such as by cutting sheets of thedesired material to size or by molding. Similarly, the pawls may beannealed to increase their strength.

It should be understood that the heavier the pawl, the more force itwill take to urge the pawl into contact with the blade or other cuttingtool within the selected time increment and the more restraining forcethat restraining mechanism 32 will need to exert to counteract thebiasing mechanism. On the other hand, the pawl must have sufficient massand strength to withstand the forces exerted upon the pawl by the blade.It should also be understood that the longer it takes for pawl 60 toengage the blade after detection of a dangerous, or triggering,condition by detection subsystem 22, the longer the blade will rotateand potentially cut the user's hand or other body part. Therefore, it ispreferred that this time be minimized, such as by decreasing thedistance pawl 60 must travel to engage the blade and increasing thespeed at which the pawl moves to travel this distance. The speed atwhich the pawl travels is largely dependent upon the weight of the pawl,the force with which biasing mechanism 30 urges the pawl toward theblade upon release of restraining mechanism 32, and any friction in themechanism.

There is not a specific pawl size, geometry or weight that is requiredto be suitable for use to stop the blade or other cutting tool. Instead,the size, geometry and weight may vary, depending upon such factors asthe particular type of machine and cutting mechanism with which the pawlis used, the pawl material or combinations of materials, thecorresponding structure of biasing mechanism 30 and restrainingmechanism 32, etc. As such, the following discussion of materials, sizesand geometries are meant to provide illustrative examples of somesuitable materials, geometries and sizes. Similarly, pawls may be formedwith any combination of one or more of the subsequently discussedelements, subelements and possible variations, regardless of whether theelements, subelements and possible variations are shown together in thesame figure.

The thickness of pawl 60 may vary. Thicknesses in the range ofapproximately ½ inch and approximately 1 inch have proven effective,although thicknesses outside of this range may be used so long as thepawl may reliably stop the blade. When thicker blades, such as dadoblades are used, the pawl is more likely to have a thickness greaterthan 1 inch.

Pawl 60 engages the blade to quickly stop the rotation of the blade.Pawl 60 may engage the blade in several different configurations, suchas engaging the side of the blade or the teeth of the blade. As shown inFIG. 3, pawl 60 is pivotally mounted on an axle 502 that extends througha bore 504 in the pawl, and pawl 60 is adapted to pivot into the teeth506 of blade 40 under the influence of a biasing mechanism, such asspring 66. The pivotal pawls described herein may alternatively pivotwith an axle upon which the pawl is secured, as opposed to pivotingabout the axle. Other suitable biasing mechanisms are disclosed incopending U.S. Provisional Patent Application Ser. No. 60/225,170,entitled “Spring-Biased Brake Mechanism for Power Equipment,” filed Aug.14, 2000 by SD3, LLC, which is incorporated herein by reference.Preferably, pawl 60 is adapted to be self-locking, i.e., drawn intotighter engagement with the teeth of blade 40 due to the relativegeometry of the blade and pawl as they are drawn together. For example,when blade 40 is spinning in the indicated direction in FIG. 3, theblade will draw the pawl into tighter engagement with the blade when theblade contacts the pawl.

The spacing from pawl 60 to blade 40 when the pawl is in its restrained,or cocked, position may vary. For example, this spacing may varydepending on the configuration of the particular cutting tool, thedetection system, and/or the brake system. Preferably, this distance isminimized to reduce the time required for the pawl to travel across thisdistance and engage the blade. It has been found that a space ofapproximately 1/32-inch to ¼-inch between the pawl and blade providessuitable results. A spacing of approximately ⅛-inch has provenparticularly effective, although larger and smaller distances may beused. Because many cutting tools such as saw blades do not haveprecisely uniform dimensions, it may be necessary to position the pawlsufficiently away from the blade to account for variations orirregularities in a particular blade, such as described in copendingU.S. Provisional Patent Application, which is entitled “BrakePositioning System,” and which is incorporated herein by reference. Alsoit may be necessary to adjust the position of the pawl whenever a bladeis replaced to account for variations between particular blades. Forexample, for circular saw blades having nominal diameters of 10-inchesand nominal thicknesses of 0.125-inch, actual blades from variousmanufacturers or for different applications may have diameters thatrange between 9.5-inches and 10.5-inches and thicknesses that rangebetween 0.075-inch and 0.15-inch.

In the illustrative embodiment of pawl 60 shown in FIG. 3, it can beseen that pawl 60 includes a body 508 with a contact surface 510 that isadapted to engage blade 40. Pawl 60 also includes an engagement member512 that is adapted to be engaged by biasing mechanism 30. As shownengagement member 512 forms part of the face 514 of the pawl that facesgenerally away from the cutting tool. Engagement member 512 may alsoinclude a recess into or protrusion from the body of the pawl. In themounting position shown in FIG. 3, pawl 60 pivots into the blade uponrelease of restraining mechanism 32, such as when the safety systemsends a current through fusible member 70. When the pawl contacts theblade, the contact surface extends generally tangential to the blade,and the teeth of the blade embed into the pawl.

Another illustrative example of pawl 60 is shown in FIG. 4. As shown,the pawl is somewhat smaller than the pawl shown in FIG. 3. An advantageof a smaller pawl is that it will be lighter than a larger pawlconstructed from the same material, and therefore it will not require asgreat of spring force to urge the pawl into the blade in a selected timeinterval as a heavier pawl. On the other hand, a smaller pawl will tendto, but not necessarily, have a smaller contact surface 510. In FIG. 4,the pawl includes a blade-engaging shoulder 516 that is adapted toengage the blade before the contact surface, or at least a substantialportion of the contact surface, engages the blade. Shoulder 514 mayinclude a protrusion 516′ that extends from the surface 518 of the pawlgenerally facing the blade. Shoulder 516 and/or protrusion 516′ engagethe blade prior to the contact surface of the pawl, and this contactquickly pivots the contact surface of the pawl into engagement with theblade. In essence, the shoulder or protrusion reduces the time and/orspring force required to quickly move the pawl into a position to stopthe blade by using the blade momentum, transferred by contact with theshoulder, to draw the pawl into the blade. Also shown in FIG. 4 isanother embodiment of engagement member 512, which as shown includes acollar 520 extending from surface 514 and into which a portion of spring66 is received. Collar 520 has an inner diameter that is greater thanthe diameter of the portion of the spring received therein. Collar 520facilitates the positioning of the spring during assembly, or cocking,of the brake mechanism.

Another illustrative example of a suitable pawl 60 is shown in FIG. 5.As shown, the pawl is somewhat larger than the previously illustratedpawls and includes a contact surface 510 that generally conforms to theouter diameter of the blade. Also shown in FIG. 5 is a mounting assembly522 for restraining mechanism 32. As shown, mounting assembly 522includes an aperture 524 through which a portion of the restrainingmechanism, such as a portion of fusible member 70, extends. Fusiblemember 70 may also be described as extending around a portion 526 of thepawl. Other suitable fusible members and restraining mechanisms aredisclosed in copending U.S. Provisional Patent Application Ser. No.60/225,056, entitled “Firing Subsystem for Use in a Fast-Acting SafetySystem,” filed Aug. 14, 2000 by SD3, LLC, which is incorporated hereinby reference.

To increase the gripping action of the pawls on the blade, the contactsurfaces 510 of the pawls may be coated with a performance-enhancingmaterial 527, such as shown in FIG. 6. An example of aperformance-enhancing material is a relatively high-friction materialsuch as rubber or a material that “tangles,” or snares, in the teeth ofthe blade or other cutting tool, such as Kevlar cloth or metal mesh.Alternatively, the pawls may be constructed of a harder material thanthe blade and have a ridged surface to “bite” into the blade.Alternatively, or additionally, the pawl may be configured with gripstructure 529 such as coatings of high-friction material, grooves,notches, holes, protuberances, etc., to further increase the grippingaction of the pawls.

Pawl 60 may include one or more removed regions. These regions may takeany suitable form, such as depressions that extend partially through thepawl or bores or other apertures that extend completely through thepawl. An example of a pawl showing plural removed regions 528 in theform of depressions 530 is shown in FIG. 7. The removed regions reducethe overall weight of the pawl, thereby decreasing the relative forcethat biasing mechanism 30 needs to exert on the pawl to move the pawlinto contact with the blade within a selected time interval, as comparedto a similar pawl of greater weight. Depressions, or recesses, 530 mayalso improve the grip of the pawl on the teeth of the blade by allowingthe teeth to bite more deeply into the pawl.

An example of another embodiment of engagement member 512 is also shownin FIG. 7 in the form of a depression 532 that extends into the body 508of the pawl and into which a portion of spring 66 extends. Depression532 may be laterally open, or may include sidewalls 534, such asindicated in dashed lines. Also shown in FIG. 7 is a mount 535 adaptedto be coupled to biasing mechanism 30. As shown, mount 535 takes theform of a projection around which a portion of a coil spring (such asspring 66 shown in FIG. 4) extends. It should be understood that mount535 may be used independent of depression 532 and/or side walls 534. Thepawl shown in FIG. 7 also shows another suitable embodiment of amounting assembly 522 for restraining mechanism 32. As shown, themounting assembly includes a mount 536 for a linkage 538, which iscoupled to a fusible member that is not physically in contact with pawl60.

The pawl shown in FIG. 7 may also be described as having a body 508 witha blade-engaging portion 540 and at least one region of reducedthickness compared to the blade-engaging portion. For example, thepreviously described depressions 530 have a reduced thickness comparedto blade-engaging portion 540. The increased thickness of theblade-engaging portion provides additional strength to that portion ofthe pawl, while the reduced-thickness portions reduce the overall massof the pawl. Pawl 60 may also be described as including one or moreribs, or supports 542 extending generally between bore 504 and bladeengaging portion 540 to strengthen the pawl.

An example of a pawl having plural removed regions 522 in the form ofapertures 544 is shown in FIG. 8. Apertures 544 reduce the comparativeweight of the pawl compared to a similar pawl that does not includeapertures or other removed regions. Apertures 544 also provide regionsinto which the material forming pawl 60 may deform, or flow, into as theblade or other cutting tool strikes the pawl. Having these deformationregions reduces the stress to the pawl as it engages the blade. Itshould be understood that the size and positioning of the removedregions 522 discussed herein are for purposes of illustration and thatthese regions may be positioned in any suitable location on the pawl ina variety of shapes, sizes and configurations.

A variation of the pawl of FIG. 8 is shown in FIG. 9, in which theapertures 544 have been filled with another material 546. It should beunderstood that some or all of the apertures may be partially orcompletely filled with material 546. For example, the body of pawl 60may be formed from one of the previously described materials, with theapertures filled with another of the previously described materials or amaterial other than those described above. As a particular example, thebody of the pawl may be formed from polycarbonate or ABS, with apertures544 filled with aluminum or another suitable metal.

Another variation of the pawl of FIG. 8 is shown in FIG. 10. In FIG. 10,pawl 60 includes a plurality of apertures 544 through which one or morewires 548 are passed. As shown, a single wire 548 is looped through theapertures and also extends across a portion of contact surface 510.Although illustrated schematically with the number of wires or wirestrands shown in FIG. 10, there may preferably be many strands of wire,such as in the range of approximately 20 and approximately 500 strands.It should be understood that a “strand” of wire is meant to refer to alength of wire extending across the pawl, such as transverse to theplane of the blade or other cutting tool, regardless of whether thestrand is connected to other strands or formed from the same unitarylength of wire as other strands. Alternatively, the wire or wires couldbe threaded through one or more of the apertures without extendingacross the contact surface. An example of a suitable material for wire548 is high tensile strength stainless steel, which is available in avariety of diameters. In experiments, diameters of 0.01 inch have proveneffective, but larger or smaller diameter wires 548, as well as wiresformed of other materials, may be used.

Other forms of composite pawls include pawls formed from two or moreregions of different materials. An example of such a composite pawl 60is shown in FIG. 11, in which the body 508 of the pawl includes a region550 of material that is a different material than the rest of the bodyand which forms at least a portion of blade-engaging portion 540. Itshould be understood that the region 550 may have a variety of shapes,including layers of generally uniform thickness, such as shown in solidlines in FIG. 11, or less uniform shapes, such as layer 550′ shown indashed lines in FIG. 11.

Pawl 60 may also be formed from composites of materials, such as bylayers of different materials or by impregnating or embedding aparticular material of construction with another material to add orenhance a desired property. For example, a thermoplastic material mayinclude a framework or dispersion of fibers or other materials. Anexample of a pawl constructed of such a composite is shown in FIG. 12,in which the body of the pawl is formed of a core material 552 intowhich a filler material 554 is added. Filler material 554 may take theform of particulates, fibers, woven fibers, pellets and the like.

Pawl 60 may also include a removable blade-engaging portion 540. Thisallows the pawl to be recharged for reuse after the pawl is used to stopblade 60 and the blade-engaging portion is damaged by the blade. Itshould be understood that “removable” means that the blade-engagingportion may be selectively removed and reattached to the rest of thepawl. An example of such a pawl is shown in FIG. 13, in which the pawlincludes body 508 and removable blade-engaging portion 540′. Portion540′ may be formed of the same or a different material or combination ofmaterials as body 508. Blade-engaging portion 540′ may be attached tobody 508 by any suitable attachment mechanism 556, which is onlyschematically illustrated in FIG. 13. Examples of suitable attachmentmechanisms 556 include interlocking portions on the body andblade-engaging portion and/or mechanical linkages coupled between thebody and blade-engaging portion.

In FIG. 14, pawl 60 includes a sheath, or cover, 558 that overlies atleast the blade-engaging portion of the pawl. Sheath 558 is formed of amaterial that enhances the pawl's ability to stop blade 40, preferablywithout damaging the blade. For example, sheath 558 may be formed ofKevlar cloth. Similarly, such a material may be embedded into thethermoplastic or other material forming pawl 60, such as schematicallyillustrated in FIG. 12. Sheath 558 may extend completely or partiallyaround the pawl, or alternatively may be partially embedded in the pawl,such as shown in FIG. 15. Furthermore, Kevlar cloth, or pieces thereofmay be embedded into the thermoplastic or other material forming thepawl, such as discussed previously with respect to FIG. 12, regardlessof whether this material extends across the blade-engaging portion ofthe pawl.

A variation of a pawl that includes sheath 558 is shown in FIG. 16. InFIG. 16, the body of the pawl defines a frame 560 that includesspaced-apart side walls 562 defining a channel 564 therebetween. Sheath558 extends across the channel and is positioned to engage and stop theblade as the pawl is urged into the blade.

When pawl 60 is mounted to pivot into engagement with a blade or othercutting tool, the pawl may include more than one pivot axis. An exampleof such a pawl is shown in FIGS. 17-19, in which the pawl is mounted ona pair of pivot arms 566. As shown, pawl 60 has an elongate contactsurface 510 that engages a large portion of the blade. Arms 566 may havethe same or different lengths, and can be mounted to pivot anchors (notshown) positioned outside or inside the perimeter of the blade. Anadvantage of a pawl with an elongate contact surface is that the forceexerted by the pawl is distributed across a larger portion of the blade,thereby allowing the blade to be stopped more quickly. The longercontact surface can also be used to reduce the chance of damage to theblade because the braking force is spread over more teeth.

In FIG. 17, arms 566 are mounted to suitable portions of machine 10distal the blade relative to pawl 60, while in FIG. 18, the arms aremounted proximate the blade relative to pawl 60. In FIG. 19, one of thepivot arms extends distal the blade, while the other extends proximatethe blade relative to the pawl. An advantage of pivot arms that extendtoward, or proximately, the blade relative to the pawl is that the pawlcannot be pivoted beyond a point after which the pawl will pivot awayfrom the blade rather than toward the blade. In the embodiment of pawl60 shown in FIG. 18, for example, the pawl will always be drawn intotighter engagement with the blade when the blade is rotating in thedirection shown and strikes the pawl.

It should be understood that the previously described axle 502 or otherstructure to which the pawls are mounted may be fixed relative to thehousing of the machine. In embodiments of the machine in which theposition of the blade is adjustable, the pawl is preferably mounted tomove with the blade as the blade's position is adjusted. This latterarrangement ensures that the pawl is maintained in a predeterminedposition relative to the blade. Similarly, the charging plates arepreferably mounted to move with either the blade or arbor to maintain apredetermined and constant spacing thereto.

Alternatively, the pawl may be mounted on a portion of the machine thatdoes not adjust with the blade, but in a mounting orientation suitablefor use with the blade regardless of the blade's mounting position. Anillustrative example of such a “stationary” pawl is shown in FIGS. 20and 21. By “stationary,” it is meant that the position of the pawl doesnot move with the blade as the relative position of the blade is moved.However, upon actuation of the reaction subsystem, pawl 60 will stillmove into engagement with the blade. Alternatively, with machines inwhich the blade may raise and lower as well as tilt, the pawl may beadapted to move with one adjustment, such as tilting with the blade, butremain fixed with the other, such as when the blade is raised orlowered.

As shown in FIGS. 20 and 21, pawl 60 is elongate and sized and shaped toextend along the outer perimeter 568 of blade 40 as the blade isadjusted vertically. Similarly the width of pawl 60 is sized to extendthe breadth of the incline of blade 40. As shown in FIGS. 20 and 21,pawl 60 is mounted generally parallel with the vertical axis of travelof the blade, and generally normal to the axis of incline of the blade.As a result, the spacing between the blade and contact surface 510remains constant regardless of the position or orientation of the blade.

The upper end portion of pawl 60 is pivotally attached to upper pivotarms 570 by pivot pins 572 that pass through one end of arms 570 intothe sides of the pawl. The other ends of pivot arms 570 are pivotallyattached to one or more mounts (not shown), by pivot pins 574. The lowerend portion of pawl 60 is pivotally attached to lower pivot arms 576 bypivot pins 578 that pass through one end of arms 576 into the sides ofthe pawl. The lower pivot arms are pivotally attached to mounts (notshown) by pivot pins 580. Biasing mechanism 30, such as one or moresprings 66, is attached to the lower pivot arms on the side of pivotpins 580 opposite pivot pins 578. Thus, pawl 60 is configured to pivottoward or away from blade 40. Upon release of restraining mechanism 32,such as fusible member 70, the biasing mechanism urges the upper ends ofpivot arms 576 downward, thereby drawing the lower end of the pivot armsand the corresponding end portion of pawl 60 into engagement with theblade.

Pivot arms 570 and 576 are sized and arranged such that pawl 60 cannotpivot up past the blade without striking the edge of the blade. When thepawl strikes the blade while the blade is rotating, the movement of theblade causes the pawl to continue pivoting upward until the pawl isfirmly wedged between the blade and pivot arms, thereby stopping theblade. The contact surface 510 of the pawl may be textured, coated,etc., to enhance the gripping action between the pawl and the blade.

Pawl 60 is biased upward to pivot toward the blade by biasing mechanism30, which for example includes one or more springs 66 that are anchoredto the saw frame or other suitable mounting structure. Thus, when thepawl is free to pivot, springs 66 drive the pawl quickly toward theblade. Fusible member 70 is connected to one or both of lower pivot arms576 to hold the pawl away from the blade. The fusible member is sized tohold the pawl spaced slightly away from the edge of the blade. However,when a sufficient current is passed through the fusible member thefusible member will melt, causing the pawl to pivot toward the bladeunder the urging of biasing mechanism 30.

It will be appreciated that many variations to the exemplary embodimentdepicted in FIGS. 20 and 21 are possible. For example, the pawl may beconfigured to pivot toward the blade solely due to gravity.Alternatively, springs 66 may be compression springs which normally holdthe pawl away from the blade until it is pivoted upward under the forceof another spring, an explosive charge, a solenoid, gas pressure, etc.Further, the pawl may be mounted on the other side of the blade to pivotdownward into the blade under the force of a spring, an explosivecharge, a solenoid, gas pressure, etc.

Another example of a suitable pawl 60 is shown in FIG. 22. As shown,pawl 60 includes a rearward portion 582 facing generally away fromcontact surface 510. Portion 582 includes a plurality of race portions584 that in cooperation with a corresponding plurality of race portions586 on a suitable mounting structure 588 forming part of machine 10,define races 590 within which rollers 592 are housed. Toothed rollers592 are rotatable within races 590 and direct the translational movementof pawl 60 toward blade 40 when the blade strikes pawl 60. The rollersalso reduce the friction of moving the pawl under braking load relativeto a sliding surface. Preferably, pawl 60 includes guide pins 593 thattravel within tracks (not shown), which define the range oftranslational positions of pawl 60 while maintaining the rollers incontact with the races.

In FIG. 23, another illustrative embodiment of a brake mechanism 28 thatincludes a pawl 60 that moves via translation into engagement with theblade or other cutting tool is shown. Pawl 60 includes a contact surfacethat preferably, but does not necessarily, conform to the outer diameterof blade 40. Pawl 60 is retained in its cocked, or restrained, positionby restraining mechanism 32, which as shown, includes one or morefusible members 70. Preferably, braking mechanism 28 includes guidestructure 501 that defines a track 503 along which the pawl travels asit is urged toward the blade or other cutting tool by biasing mechanism30. An example of such a guide structure is shown in FIG. 23, in whichthe guide structure includes a housing 505 into which the pawl is atleast partially received in its cocked, or restrained position, and fromwhich the pawl at least partially projects upon release of restrainingmechanism 32. Much like a piston moving within a cylinder, pawl 60travels in a translational path defined by the inner dimensions ofhousing 505 under the urging of biasing mechanism 30.

Other illustrative examples of brake mechanisms 28 with translationalpawls are shown in FIGS. 24 and 25. In FIG. 24, guide structure 501includes two or more guide-engaging members 507 that project from pawl60 to engage a corresponding number of guides 509. Guides 509 are spacedapart from the pawl and define the translational path of the pawl. InFIG. 25, pawl 60 includes internal guide-engaging members 507, such asone or more internal bores 511 extending parallel to the translationalpath of the pawl. A corresponding number of guides 509 extend at leastpartially within the bores to define the travel path of the pawl. InFIGS. 23-25, pawls 60 are urged along a translational path directly intoblade 40. It should be understood that the pawls and/or the guidestructure may be inclined at an angle relative to the blade, such as tocounteract the angular momentum of the blade or to utilize the brakingforce to draw the pawl more tightly against the blade.

Although the exemplary embodiments are described above in the context ofa single brake pawl that engages the teeth of a blade, the brake systemmay incorporate a brake mechanism with two or more pawls that engage twoor more locations on the perimeter of the blade to decrease the stoppingtime and/or spread the stopping forces. An example of such a brakemechanism is shown in FIG. 26, in which the brake mechanism includes twospaced-apart pawls 60 adapted to engage the perimeter of blade 40. Pawls60 are only schematically illustrated in FIG. 26 and could include anyof the previously described pawl or pawls incorporating one or more ofthe features, elements, subelements and variations described above. Thepawls may be released from their cocked, or restrained, positions by acommon release mechanism, or each pawl may have its own releasemechanism. When brake mechanism 28 includes plural pawls, it may bedesirable to position the pawls on opposite sides of the arbor aboutwhich the blade rotates to reduce the load on the arbor when the brakemechanism is actuated and the pawls engage the blade.

When brake mechanism 28 includes plural pawls, the pawls may also beconstrained or interconnected to act together. An example of such abrake mechanism is shown in FIG. 27, in which the brake mechanismincludes a plurality of interconnected pawls 60. As shown, each pawl 60includes one or more toothed regions 513 having a plurality of teeth515. Regions 513 of adjacent pawls 60 are interconnected by toothedgears, or linkages, 517 that communicate the rotation of one pawl to theother pawls so that the pawls move as a unit. It should be understoodthat one or more of the pawls or gears are coupled to a suitable biasingmechanism and restraining mechanism to bias the pawls into contact withblade 40 and to selectively restrain the movement of the pawls until thereaction subsystem is actuated. In a variation of the brake mechanismshown in FIG. 27, gears 517 may be omitted, in favor of linksinterconnecting the pawls.

As discussed, the pawl or pawls of brake mechanism 28 may contact anysuitable portion of blade 40 or other cutting tool 14. In theillustrative embodiments shown in FIGS. 2-27, the pawls were mounted toengage the teeth or outer perimeter of the blade. An example of anothersuitable contact portion of the blade is the side of the blade.Specifically, brake mechanism 28 may include two or more pawls adaptedto engage opposed sides of the blade. An example of such a brakemechanism is illustrated in FIG. 28. As shown, pawls 60 are pivotallymounted on either side of blade 40. Each pawl includes a blade-engagingportion 540 adjacent the blade, and a distal portion 519. The pawls arepivotally mounted on pins 521 that pass through pivot apertures 523 inthe pawls intermediate the blade-engaging portion and the distalportion. Lever arms 525 are coupled to distal portions 519. Thus, whenthe lever arms of each pawl are pivoted upward (as viewed in FIG. 28),the blade-engaging portions close together. The pawls are mountedrelative to the blade so that the contact surfaces pivot toward theblade in the direction of blade travel. Once the pawls contact and gripthe blade, they continue to pivot inward pulled by the downward motion(as viewed in FIG. 28) of the blade. As a result, the blade is pinchedmore and more tightly between the contact surfaces 510 of the pawlsuntil the pawls can close no further, at which point the blade isstopped between the pawls.

To ensure that both pawls close together on the blade, a linkage 527 isattached, at one end, to lever arms 525. Linkage 527 is coupled to abiasing mechanism, not shown, which urges the pawls into contact withthe blade, through force exerted through linkage 527 and lever arms 525.

It will be appreciated that the dual-pawl system described above may beimplemented with many variations. For example, the linkage may be drivenupward by any of the other actuating means described above, including anexplosive charge, solenoid, compressed gas, etc. As another example, oneor more pawls may be positioned to contact only one side of the blade.Additionally, the linkage may be omitted, and each pawl actuated by aseparate spring, explosive charge, solenoid, etc. Similarly, although acircular blade 40 was used to illustrate one type of cutting tool forwhich the brake system may be used, it may also be used with othershapes of blades, such as blades used in jointers, shapers and bandsaws.

As mentioned above, safety system 18 may include a brake mechanism thatis adapted to stop a cutting tool upon the detection of a dangerouscondition, thereby preventing or reducing injury to the user. As alsomentioned above, brake mechanism 28 may include at least one brake pawladapted to engage and stop the motion of the cutting tool. In brakemechanisms that include a brake pawl, a significant impact occurs whenthe brake pawl engages the cutting tool because of the speed at whichthe cutting tool typically moves. The resulting force of that impact maydamage the machine in which the brake mechanism is installed, and/or theimpact may damage the cutting tool. For example, in a table saw or mitersaw having a spinning blade mounted on an arbor (like shaft 42 in FIG.2), the force of the impact between the blade and the brake pawl maybend the arbor, thereby damaging the saw. The likelihood of damaging amachine or cutting tool from the force of the impact may be reduced byusing a brake pawl that includes a collapsible or deformable regionconfigured to absorb some of the energy and/or force of the impact.

FIG. 29 shows a brake pawl 1102 having an energy absorbing region 1104designed to deform or collapse when the pawl impacts a cutting tool. Thedeformation of region 1104 helps the pawl absorb the energy of thespinning cutting tool and the force from the impact with the cuttingtool, thereby reducing the likelihood that the impact will damage otherparts of the machine or the cutting tool. In FIG. 29, region 1104comprises a series of holes extending through the pawl, such as holes1106. Of course, the number, size and configuration of the holes mayvary. The holes create what may be thought of as a structurally weakerregion of the brake pawl. Pawl 1102 is designed to be mounted on a pivotpin extending through pivot hole 1108. When the pawl impacts a spinningblade, for example, the blade cuts into the pawl and pushes the pawlagainst the pivot pin extending through hole 1108, causing region 1104to deform or collapse and thereby absorb at least a part of the energyof the spinning blade. Typically the deformation will be a compressionof region 1104, as shown in FIG. 30, but the pawl may also bend ordeform around region 1104. The compression of region 1104 is shown inFIG. 30 by wrinkles in the pawl, such as wrinkles 109, and by holes 1106being closer together and elliptical.

FIG. 31 shows a brake pawl with another possible configuration for adeformable or collapsible region 1104. In this configuration, region1104 comprises an elongate aperture 1110. The aperture is positionedadjacent pivot hole 1108, and aperture 1110 collapses as shown in FIG.32. The collapse of that aperture absorbs some of the energy of thespinning cutting tool when the pawl impacts the cutting tool, therebyreducing the likelihood of damaging a machine or cutting tool.

In some cases it may be desirable to position the deformable orcollapsible region at an angle relative to the elongate axis of thepawl, as shown in FIG. 33. Positioning the deformable or collapsibleregion at an angle may be desirable in order to position the regionbetween the point of impact of the cutting tool with the pawl and thepivot pin on which the pawl is mounted, so that the deformable orcollapsible region is in line with the direction of force. Additionally,it is believed that the position of the deformable or collapsible regionmay affect how well the pawl grips the cutting tool when the cuttingtool cuts impacts and cuts into the pawl.

FIG. 34 shows another possible configuration for a deformable orcollapsible region 1104. In FIG. 34, brake pawl 1102 includes a firstportion 1112 and a second portion 1114. A collapsible member 1116 joinsthe first and second portions of the brake pawl. Collapsible member 1116may be made from a material that is different from the brake pawl. Forexample, the brake pawl may be made of aluminum, and the collapsiblemember may be made of a less hard aluminum or some other material suchas urethane; or the brake pawl may be made of a hard plastic materialand the collapsible member may be made of a softer, more compressible ordeformable material. Collapsible member 1116 may compress and/or bulgeout between the first and second sections of the brake pawl when thepawl contacts a cutting tool.

FIG. 35 shows a brake pawl similar to the one shown in FIG. 34, exceptthat the collapsible region 1104 comprises two collapsible members 1116instead of one.

FIG. 36 shows another possible configuration for a deformable orcollapsible region 1104. In FIG. 36, brake pawl 1102 includes a “T”shaped end 1118 having members 1120 and 1122 mounted in brackets 1124and 1126, respectively. The brackets, in turn, are mounted in a machine.When the pawl contacts a cutting tool, the force of the impact maydeform the “T” shaped end 1118 by bending members 1120 and 1122, asshown in dashed lines in FIG. 36.

Of course, there are many possible configurations for deformable orcollapsible regions, and only a few are discussed above. Variousapertures, collapsible members, materials, etc. may be used. Thedeformable or collapsible regions also may be thought of asenergy-absorbing regions.

It also may be desirable to form brake pawls out of annealed aluminum tomake the aluminum softer. Aluminum stops cutting tools quickly, andannealing the aluminum seems to lessen the likelihood that the aluminumwill damage the cutting tool or machine upon impact with the cuttingtool. For example, it is believed that an annealed aluminum brake pawlis less likely to knock teeth off a circular saw blade than an aluminumbrake pawl which has not been annealed.

It is believed that the disclosure set forth above encompasses multipledistinct inventions with independent utility. While each of theseinventions has been disclosed in its preferred form, the specificembodiments thereof as disclosed and illustrated herein are not to beconsidered in a limiting sense as numerous variations are possible. Thesubject matter of the inventions includes all novel and non-obviouscombinations and subcombinations of the various elements, features,functions and/or properties disclosed herein. No single feature,function, element or property of the disclosed embodiments is essentialto all of the disclosed inventions. Similarly, where the claims recite“a” or “a first” element or the equivalent thereof, such claims shouldbe understood to include incorporation of one or more such elements,neither requiring nor excluding two or more such elements.

It is believed that the following claims particularly point out certaincombinations and subcombinations that are directed to one of thedisclosed inventions and are novel and non-obvious. Inventions embodiedin other combinations and subcombinations of features, functions,elements and/or properties may be claimed through amendment of thepresent claims or presentation of new claims in this or a relatedapplication. Such amended or new claims, whether they are directed to adifferent invention or directed to the same invention, whetherdifferent, broader, narrower or equal in scope to the original claims,are also regarded as included within the subject matter of theinventions of the present disclosure.

1. A power tool comprising: a moving cutting tool, a safety systemadapted to detect a dangerous condition between a person and the cuttingtool, and a brake pawl adapted to engage the cutting tool upon detectionby the safety system of the dangerous condition, where the brake pawlincludes a contact region adapted to engage the moving cutting tool andan energy-absorbing region adapted to absorb at least some of the energyof the moving cutting tool by permanently deforming or collapsing whenthe contact region engages the moving cutting tool.
 2. The power tool ofclaim 1 where the energy-absorbing region comprises at least one hole.3. The power tool of claim 1 where the energy-absorbing region comprisesholes.
 4. The power tool of claim 1 where the brake pawl includes amounting region distinct from the contact region and where theenergy-absorbing region is nearer the mounting region than the contactregion.
 5. The power tool of claim 1 where the brake pawl includes amounting region adapted to mount the brake pawl on a pin.
 6. The powertool of claim 1 where the energy-absorbing region comprises an elongateaperture.
 7. The power tool of claim 1 where the brake pawl includes amounting region adapted to mount the brake pawl on a pin and where theenergy-absorbing region comprises an aperture adjacent the mountingregion.
 8. The power tool of claim 1 where the brake pawl includes amounting region and where the energy-absorbing region is between thecontact region and the mounting region.
 9. The power tool of claim 1where the energy-absorbing region is shaped to deform or collapse. 10.The power tool of claim 1 where the energy absorbing region is shapedlike a “T” with two ends, and where the where the two ends are adaptedto mount in brackets.
 11. The power tool of claim 1 where theenergy-absorbing region is annealed aluminum.
 12. The power tool ofclaim 1 where the contact region is annealed aluminum.
 13. The powertool of claim 1 where the energy-absorbing region comprises at least onedepression.
 14. The power tool of claim 1 where the energy-absorbingregion is structurally weaker than another region of the brake pawl. 15.The power tool of claim 1 where the contact region includes at least onehole and the energy-absorbing region comprises at least one hole. 16.The power tool of claim 1 where the contact region includes holes andthe energy-absorbing region comprises at least one hole.
 17. The powertool of claim 1 where the brake pawl includes a mounting region distinctfrom the contact region, where the contact region includes at least onehole, and the energy-absorbing region is between the contact region andthe mounting region.
 18. The power tool of claim 1 where the contactregion and the energy-absorbing region overlap.
 19. The power tool ofclaim 1 where the contact region and the energy-absorbing region areseparate.
 20. A power tool comprising: a moving cutting tool, a safetysystem adapted to detect a dangerous condition between a person and thecutting tool, and a brake pawl adapted to engage the cutting tool upondetection by the safety system of the dangerous condition, where thebrake pawl includes a contact region adapted to engage the movingcutting tool and means for permanently deforming or collapsing to absorbat least some of the energy of the moving cutting tool when the contactregion engages the moving cutting tool.